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I have looked up a manual for repair of S6 and it seems to state that there are 2 different contant/zero error/correction settings for the S6 Dr 300+. These are determined in the factory and entered into S6 memory. Apparently the high precision model and S8 hp have the same constant/zero errors/corrections for Standard meas and DR meas unlike the

older regular models. Maybe this is the case for more recent vintage S6,S5,S7,S9 etc., i.e there is only one zero error correction in instr.

Interestingly (or maybe not...) there is also a correction for short range distances <12m. Apparently too much signal coming back. So if doing precise work or checks on instrument

and if so one presumes that these errors are small and typically less than 1.5mm in amplitude and instruments

that quote 2mm plus xxppm must surely have this amplitude down to less than 1mm.

Again the high precision instruments must have a lower amplitude sub 0.5mm.

Does this matter....In most cases probably not. But I found over the years that when doing more demanding work,

my Traverses didn't close quite as good as they should have. EDM (Total Stn) seems to compare well with Fast Static

GPS but traverses just aren't closing way they should. This was with 3-4 different instruments.(I hear you say, funny enough, that maybe I am the constant that is not up to scratch.) but, I have recently got the time to do some checks on

3 different sets of prisms (2 of them Trimble) for constant error and none of this prisms are coming in good. [ 2x 32mm Trimble RMT 602, 2 No. AGA Geodimeter Super prisms and 2 No Topcon Prisms]. All prisms looking consistently out.

Leads me to believe that the "issue" is maybe with the constants typed into the S6 which are probaly incorrect.

Connection between Constants for Instr/prism and cyclic errors, is that in order to determine correct constant error you really need knowledge of the period and amplitude of cyclic error. This will hopefully enable us to determine a correct

constant error which we can print onto our prisms (housing) and hopefully adjust the standard offsets that we type in for various prisms in use. Then maybe our traverses will close a little better.

I have run some of my own tests on cyclic error in S6's using a 1m steel precise rule on a bench and running

602 rmt prism along rule to determine any evidence of periodic error in EDM. The resolution of these instruments is very good and coupled with 2-3 mins measure time precision at 0.1 to 0.2mm is achievable as proven by bench test.

By comparing relative differences of observations along rule at 0.05m & 0.1m intervals it was possible to plot systematic

(appears to be) deviations from truth as given by precise KDS rule.

The amplitude of the error is +/- 0.3mm for S6 tested. This would make sense in terms of Manufactures' quoted accuracy. The period would seem to be 0.6m, thus confirming 1.2 pulse width for TOF instr. The S6 sends out a pulse

1.2m long and waits for return signal then sends another pulse. Does this every 40 millionths of a second.

For my exercise on determining accurate prism constant errors this size of error won't make an enormous difference but

but hopefully I can use info to eliminate the effect of cyclic error in determining constant errors for my prisms.

It is somewhat difficult to get information of this nature from Trimble and often instruments are just sold with 360 prisms

which we know have limitations. It is important to know what prism the stored Constant Errors refer to.